Telephone system



c. E. LoMAx TELEPHONE SYSTEM Filed Dec. 24,' 195s June 24, 1941.

Patented June 24, 1941 TELEPHONE SYSTEM Clarence E. Lomax, Oak Park, Ill'., assignor towAs sociated Electric Lalioratories,y Inc., Chicago, Ill'., a corporation of Delaware Application December 24, lesaseriai No., 247,603

33 Claims.

The present invention relates to signaling systems and more particularly' to :telephone systems comprising a number of. remotely disposed exchanges interconnected by trunk lines. Y

A telephone system conventionally comprises two or more main exchanges and one or more.

auxiliary exchanges interconnected by trunk lines terminating at operator' positionsv in the respective exchanges. Usually, one or more through trunk `lines extend between the two main exchanges; and one or more branch trunk:` lines extend between the auxiliary exchange and a central point disposed intermediate the two `main exchanges, the branch trunk `lines being tapped onto the respective through trunk lines.` vOrditype and comprisesv suitable apparatus for setting up trunk connections byway of any 4one of the trunk lines terminating therea-t.

While reasonably satisfactory trunk service may be rendered in a telephone system of the type described,y there are several objectionable features thereto. positions disposed in the three exchanges 'mentioned are interconnected by each trunkline,

rendering it necessary to employ code ringing in the system order that a calling operator may indicate to the other two operators which one of them is the sailed operator. A more seri--` ously objectionabie feature of the system resides in the fact that the portion of each through trunk line disposed on either point and the branch trunk line connected to the through trunk line at the tapped point are electrically interconnected. Accordingly, aV fault upon: the branch trunk line renders the through trunk line out of service. Likewisea fault on either of the portions mentioned of the through trunk line renders the branch trunk line outof service. Moreover, the branch trunk line'unnecessarily increases the transmission losses upon the through trunk line when a trunk connection is established between the main exchanges. Likewise, one portion mentioned of` the through trunk line unnecessarily increases the transmission losses upon the branch trunk line and the other portion mentioned of the through trunk` line wh-en a` trunk connection is established between theauxiliary exchange and one of the main exchanges.

Accordingly, it is an object. of the present in- In the first place,` the operator" side of a tapped' 1.5 narily, each operator :position is lci the manual.

pendent trunk lines extending between the switching center and a number of exchanges.

Another object of the invention is to provide,

in a telephone system comprising a number oi i exchanges and a switching center, an improved arrangement controlledover a calling trunk line extending between one of the` exchanges and the switching center for Vselectively associating the calling trunk line with other of the trunk lines `extending between the switching center and other of the exchanges.

A further object `of the. invention is to provide, in a telephone system of the type noted, an irnproved switching arrangement and control arrangement therefor at the switching center for selectively interconnecting the trunk lines extending-between Ythe switching center and the exchanges. -f Y The features of the present invention are illus-- trated as being incorporated in a telephone system comprising a switching center, three exchanges and trunk lines extending between the switching .center and the respective exchanges, each of the trunk lines comprising two line con..

; ductors, one end of each trunk line being terminated in a repeater at the switching center and the other end thereof being terminated in a repeater`- in the exchange to which the trunk lineY extends. Also an operator postionisarranged j, in `each of the exchanges` and providedwith suitable apparatus fcr initiating and answering trunk calls and for setting up trunk connections over the trunklines extending to the associated exchange. ,Furthermore,.-switching apparatus is fprovided ati the switching center which is selectively operative to associate any one of the repeaters thereat with two other of the repeaters thereat, Vthereby .selectively and operatively -to connect Vthe trunk line terminated by the one` `repeatervtothe two trunk lines terminated by the two other repeaters.

`In accordance with one feature of the invention,` the: switching apparatus` at the switching center comprises `a plurality of relay devices re.-

,spectively associated with the repeaters at the switching center and individually provided with control apparatus. More particularly, each of the control apparatus includes a circuit network; and each of the relay devices comprises two relays respectively provided with operating windings, the operating windings of the two relays being so connected and arranged in the asso-4 ciated control apparatus that the two relays are selectively operative in accordance with the direction of current flow in the circuit network of the associated control apparatus. In a given relay device, one of the relays is operative to cause the associated repeater at the switching center to be associated with another repeater thereat; while the other of the relays is operative to cause the associated repeater at the switching center to be associated with a further repeater thereat. Accordingly, the given relay device is selectively operative to connect the trunk line terminated by the associated repeater operatively and selectively to the two trunk lines terminated respectively by the other and the further repeaters mentioned.

Moreover, the circuit network of each of the control apparatus is provided with two terminals, one of which is connected to ground and the other of which is connected to a corresponding simplex link provided by the associated repeater at the switching center, the trunk line terminated by the last-mentioned repeater and the repeater in the exchange to which the last-mentioned trunk line extends.

In accordance with another feature of the invention the control apparatus provided at each operator position comprises a cord circuit including a telephone instrument and talk and ring keys, means for operatively associating the cord circuit with the trunk line extending to the associated exchange and means for selectively connecting the ungrounded positive terminal of a grounded source of current and the ungrounded negative terminal of a grounded source of current to the simplex link provided by the toll line extending to the associated exchange. More particularly two call jacks are provided at the operator position and associated with a loop circuit extending to therepeater in the associated exchange terminating the trunk line extending thereto; and thecordcircuit at the operator position is provided with a plug. When the plug of the cord circuit is selectively inserted into the two call jacks the cord circuit, and consequently the telephone instrument therein, are operatively associated by way of the loop circuit and the repeater with the trunk line extending to the associated exchange and the positive and negative terminals of the sources of current are selectively connected to the simplex link mentioned, thereby selectively to determine the direction of the current conducted to the circuit network of the control apparatus connected to the simplex link. Also, the ring and talk keys in the cord circuit are operative respectively to control the projection of alternating signal current over the trunk line extending from the exchange and over the trunk line operatively associated with the last-mentioned trunk line at the switching center and to control the connection of the telephone instrument inthe cord circuit to the loop circuit mentioned. Furthermore, an answer jack and a signal are provided at each operator position for the respective purposes of answering a trunk call extended to the associated exchange and of signaling the operator when a trunk call is extended to the associated exchange.

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additional features are attained.

The-'novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which the single figure illustrates diagrammatically a telephone system having embodied therein the features of the present invention.

Referring now more particularly to the drawing, the telephone system there illustrated comprises a switching center Ill, three remotely disposed manual telephone exchanges A, B and C and three toll or trunk lines 80, 'Hl and 50, respectively extending between the switching center I0 and the exchanges A, B and C. Each of the toll lines is of the two-way type and the opposite ends thereof are terminated in repeaters disposed at the switching center I and in the exchange to which the toll line extends. More particularly, the ends of the toll lines t5, 'I and 85) extending to the switching center Il are terminated in the repeaters 64, 'i4 and 84, respectively, disposed at the switching center Il); while the ends of the toll lines t0, 'I0 and 8l) extending to the exchanges C, B and A are respectively terminated in the repeaters I3, Il and I5 disposed in the respective exchanges. A toll operator position in each of the exchanges is operatively associated with the repeater in the exchange terminating the toll line extending thereto. More particularly, the toll operator positions I4, I6 and I2 in the exchanges A, B and C, respectively, are operatively associated with the repeaters I5, II and I3, respectively terminating the toll lines 80, 'I0 and 60 extending to the respective exchanges.

The repeaters 84, I4 and Sil at the switching center IIJ are operatively associated with a switching network thereat including three groups of relays, each group comprising two relays. More particularly, the repeater 84 is operatively associated with a group of relays comprising the relays R90 and R95; the repeater 'I4 is operatively associated with the group of relays comprising the relays RI IU and RI I5; and the repeater 64 is operatively associated with the group of relays comprising the relays RI 00 and RIB5. A unidirectional current conducting device in the form of a copper oxide rectifier is connected in parallel circuit relationship with the winding of each of the relays R90, R95, RIEN), etc., the devices 9|, 96, IDI, |06, III and IIB being respectively connected in parallel circuit relationship with the windings of the relays R90, R95, RIM, RIU5, RIII) and RII5. A circuit including a simplex link is provided for controlling the energization of the two relays in each of the groups, in a manner more fully described subsequently. The circuit for controlling the energization of the relays R90 and R95 comprising one of the groups includes a simplex link provided by the toll line and the repeaters I 5 and 84 associated therewith; the circuit for controlling the energization of the relays RIIlIl and R|II5 comprising another of the groups includes a simplex link provided by the toll line 60 and the repeaters I3 and 64 associated therewith; and the circuit for controlling the energization of the relays RIID and RII5 comprising another of the groups includes a simplex link provided by the toll line 'I0 and the repeaters I'I and 'I4 associated therewith. It is noted that the switching network at the switching center I Il is so connected and arranged that it is operative under the control of the toll operator in any one of the exchanges to connect the toll line extending to the one exchange to either one of the toll lines extending to the other exchanges.

l Each of the toll -operator positions in the exchanges A, B and C may be identical `to `the toll operator position I2 in the exchange C, which comprises two call jacks 30 and 40,fan answer jack 2|), a signal 24 and a cord circuit 50 of conventional connection and arrangement and provided with talk and ring switches or keys, not shown, a telephone instrumentnotshown, and a plug 5I adapted to be selectively inserted into the jacks 20, 30 and 40. It is noted that the jack at the operator position I2 comprises means for controlling the operation of the signal 24 thereat; while thejacks and 4I) comprise means for controlling `the operationof the relays RIOB and RI85 `in one of the groups in the switching network at the switching center II). Similarly, the respective jacks at the toll operator positions I4 and I6 comprise means for controlling the signals thereat and means for `controlling the operation of the* relays in the other groups in the switchingnetwork at the switching center IIJ. More particularly, the jacks noted at the toll operator position I4 comprise means for controlling the operation of the relays R30 and R95 comprising one of the groups in the switching network` at the'switching center I0 while the jacks notedat the toll operator position I6 comprise means for controlling the operation of the relays RI I0 and RI I 5 `comprising another of the groups in the switching` network at the` switching center Il). j

The connection and arrangement of the telephone system will best be understood `from a consideration of the following description of the operation of the apparatus incorporated therein in order to establish connections between the various toll lines 'in the system.

A call which is to be extendedfrom the exchange C to the exchange A` is initiated by the toll operator at the operator `position l2 in the exchange C upon inserting the plug 5I of the cord circuit 5D thereat` into the call jack 38. When the'plug 5I is inserted into the call jack30 the switch springs33 and`34 thereof are actuated into engagement, thereby to connectthe negative terminal of `the, battery 35, the positive terminal of which is grounded, to the conductor C21. When the ungroundedfnegative terminal of the battery 35 is connected to theconductor C21 a circuitincluding a simplex linkV provided by the toll line `6I) and the repeaters 64 and I3 `associated therewith is completed for energizing the relay Rlll. The last-,mentioned circuit extends from the grounded'positive terminator the bati tery `35 by way` of the conductor C109,` the rectifier IE6, the winding of the relay RIUD, and the conductor C63 Vto the neutral point between the windings 61 and '68 of the repeater B4, and from the negative terminal of the battery 35 by way of the switch springs 34 and 33 of the call jack 3l'I and the conductor C21 to the neutral point between the windings 31 and 38 of therepeater I3, the neutral `points mentioned being connected together byV way of a simplex circuit A' extending from the inst-.mentioned neutral point by way of the winding 81 of the repeater 64, the line con` ductor C'lv of the toll line 60 and the winding 31 of the repeater I3 to the last-mentioned neutral point, and from the frst-mentioned neutral point by way of the winding 68 of the repeater 64, `the line conductor C62 of the toll line B0, and the winding 39 of the repeater I3 tol the lastrnentioned neutral point. lt is noted that the rectifier |86 readily conducts current over 1 the above-traced circuit in the direction indicated,

thereby effectively to short-circuit the winding of the relay RI05; while the rectier IOI blocks the passage of current therethrough when current'- is conducted over the above-traced circuit inthe direction indicated. Accordingly, at this time, the relay RI U5 is not operated and the relay RI 00 is operated. Uponoperating, the relay RIU!) completes, at RAIIJZ and at RAI03, a loop circuit extending between the windings 81 and 88 of the repeater 84 land the windings 35 and `(it of the repeater `64. The last-mentioned loop circuit extends from the conductor C |20 by way ofthe windings 81 and 88 of the repeater 84, the conductor (H23, RAIBS, the conductor CI24, the windings 66 and 65 of the repeater 84, the Vcon-- ductor CTI2I and RAIIIZ to the conductor CI20.

After inserting the plug 5I of the cord circuit `5I! into the call jack 30, the toll operator at the operator position I2 actuates the talk key in the cord circuit 58, thereby to complete a loopcircuit between the telephone instrument in the cord circuit and the windings 35 and 38 of theV repeater I3. The last-mentioned loop cir-` cuit extends from the conductor C25 by way of the windings 36 and 38 of the repeater I3, the' conductor C26, the jack ring 32, the plug ring 53, the talk key and the telephone instrument in the cord circuit 5U, the plug tip 52 and the jack tip 3I to the conductor C25.

At this time a connection is established between the telephone instrument in the cord circuit 50 atthe operator position l2 and the toll line 8B extending to the exchange A, the loop Circuit, including the telephone instrument in the cord circuit 50 at the operator position I2, being" operatively associated with the previously traced loop circuit, extending between the windings I81` and 88 of the repeater B4 and the windings 65 and '66 of the repeater 64, by way of a loop tcir-- cuit extending from the line conductor CSI of the toil line 80 over the windings 51 and `(i8 o f the repeater 64, the line conductor C62 of the toll` line and the windings 39 and 31 of the repeater I3 to the line conductor CEI. Also the windings 81 and 88 of the repeater 84 are operatively assofV ciated with `the windings 85 and 85 thereof connected to the toll line extending `to the exchange A. In the event the toll line 80 is busy at this time, voice frequency current is diverted L therefromby way of the various loop circuits previously `traced to the receiver of the telephone instrument in the cord circuit 5I] at the operator position I2 and the `toll operator thereat hears the conversation.

A On the other hand, in the event the toll line 83 is idle at this time, the toll operator at the operator` position I2 does not hear a conversation. The toll operator 'at the operator position I2 then actuates the ring key` in thecord circuit 50 thereat, thereby to complete a circuit for con-v ducting lalternating ringing current over a4 portion of the previously traced loop circuit extending between the windings 36 and 38 of the` repeater I3 and the cord circuit 50. Moreparticularly, the alternating ringing current is conducted from one terminal of a source of alternating ringing current by way of the ring key in the cord circuit` 50, the plug tip 52the jack tipV 3i, the conductor C25, the windings 36 and 38 of the repeater I3,

.l the conductor C26, the jack ring 32 and the plug ring 53 lto the other terminal of the source of alternating ringing current. The alternating ringing current traversing the windings 3'6 and 38o! the repeater I3 induces a similar alternating ringing -current in the windings 31 and 39 Aofthe repeater I3 which ringing currentl traverses the previously traced loop circuit extending between the windings 31 and 39 of the repeater I3 and the windings 61 and 68 of the repeater 64. The alternating ringing current traversing the windings 61 and 68 of the repeater 64 induces a similar alternating ringing current in the windings 65 and 66 of the repeater 64 which ringing current traverses the previously traced loop circuit extending between the windings 81 and 88 of the repeater 84 and the windings 65 and 66 of the repeater 64. The alternating ringing current traversing the windings 81 and 88 of the repeater 84 induces a similar alternating ringing current in the windings 85 and 86 of the repeater 84 which ringing current traverses a loop circuit extending between the windings of the repeater I and the windings 85 and 36 of the repeater 64. The alternating ringing current traversing the last-mentioned windings of the repeater I5 induces a similar alternating ringing current in the associated windings of the repeater I5 which ringing current traverses a loop circuit extending between the last-mentioned windings of the repeater I5 and the winding of the signal at the operator position I4. 'Ihe alternating ringing current traversing the winding of the signal at the operator position I4 actuates the signal, thereby to indicate to the toll operator at the operator position I4 that a call is extended to the exchange A.

The toll operator at the operator position I4 answers the call by inserting the plug of the cord circuit thereat into the answer jack at the operator position I4. When the plug of the cord circuit is inserted into the answer jack at the operator position I4 the previously mentioned loop circuit for energizing the winding of the signal thereat is interrupted, thereby to arrest further operation of the signal. Finally, the toll operator at the operator position I4 actuates the talk key in the cord circuit thereat, thereby to complete a loop circuit between the windings of the repeater I5 and the telephone instrument in the cord circuit at the operator position I4. At this time a two-way communication connection is established between the telephone instrument in the cord circuit 50 at the operator position I2 and the telephone instrument in the cord circuit at the operator position I4, thereby to permit the toll operators at the operator positions I2 and I4 in the exchanges C and A, respectively, to communicate with each other in either direction.

The release of this established connection between the exchanges C and A is primarily under the control of the toll operator at the operator position I2 in the exchange C and is effected by the toll operator thereat by removing the plug 5I of the cord circuit 5D from the call jack 3U. When the plug 5I is removed from the call jack 30 the switch springs 33 and 34 thereof are actuated into disengagement, thereby to interrupt the previously traced path for connecting the ungrounded negative terminal of the battery 35 to the conductor C21. When the ungrounded negative terminal of the battery 35 is disconnected from the conductor C21, the previously traced circuit including the simplex link provided by the toll line 6|] and the windings of the repeaters 64 and I3 associated therewith for energizing the winding of the relay RIG!) is interrupted, whereupon the relay RIOB restores. Upon restoring, the relay RIOB interrupts, at RAIDZ and at RAI03, the previously traced loop circuit extending between the windings 81 and 88 of the 75 repeater 84 and the windings 65 and 66 of the repeater 64. Finally, the toll operators at the operator positions I4 and I2 actuate the talk keys in the respective cord circuits thereat in order to disconnect the telephone instruments therein from the plugs of the respective cord circuits at the respective operator positions.

A call which is to be extended from the exchange C to the exchange B is initiated by the toll operator at the operator position I2 in the exchange C upon inserting the plug 5I of the cord circuit 56 thereat into the call jack 46. When the plug 5I is inserted into the call jack 40 the switch springs 43 and 44 thereof are actuated into engagement, thereby to connect the positive terminal of the battery v45, the negative terminal of which is grounded, to the conductor C21, When the ungrounded positive terminal of the battery 45 is connected to the conductor C21 a circuit including the previously mentioned simplex link providedy by the toll line 66 and the repeaters 64 and I3 associated therewith is completed for energizing the relay RI05. The lastmentioned circuit extends from the ungrounded positive terminal of the battery 45 by way of the switch springs 43 and 44 of the call jack 40 and the conductor C21 to the neutral point between the windings 31 and 39 of the repeater I3, and from the neutral point between the windings 61 and 68 of the repeater 64 by way of the conductor C63, the rectifier IUI, the winding of the relay RI05 and the conductor CI09 to ground, the neutral points mentioned being connected together by way of a simplex circuit extending from the first-mentioned neutral point by way of the winding 31 of the repeater I3, the line conductor CEI of the toll line 60 and the winding 61 of the repeater 64 to the last-mentioned neutral point, and from the rst-mentioned neutral point by way of the winding 39 of the repeater I3, the line conductor C62 of the toll line 60 and the winding 68 of the repeater 64 to the last-mentioned neutral point. It is noted that the rectifier IBI readily conducts current over the abovetraced circuit in the direction indicated, thereby eiectively to short-circuit the winding of the relay RIllIl; while the rectifier |66 blocks the passage of current therethrough when current is conducted over the above-traced circuit in the direction indicated. Accordingly, at this time, the relay RIDI) is not operated and the relay R105 is operated, Upon operating, the relay RIOS completes, at RAI61 and at RAI08, a loop circuit extending between the windings 11 and 18 of the repeater 14 and the windings 65 and 66 of the repeater 64. The last-mentioned loop circuit extends from the conductor CI22 by way of the windings 11 and 18 of the repeater 14, the conductor CI25, RAIU8, the conductor CI24, the windings 66 and 65 of the repeater 64, the conductor CI2I and RAII11 to the conductor CI22.

After inserting the plug 5I of the cord circuit 58 into the call jack 46, the toll operator at the operator position I2 actuates the talk key in the cord circuit 50, thereby to complete a loop circuit between the telephone instrument in the cord circuit 50 and the windings 36 and 38 of the repeater I3. The last-mentioned loop circuit extends from the conductor C25 by w-ay of the windings 3G and 38 of the repeater I3, the conductor C26, the jack ring 42, the plug ring 53, the talk key and the telephone instrument in the cord circuit 50, the plug tip 52 and the jack tip 4I to the conductor C25.

At this time a connection is established berepeater 64.

auch@ tween the telephone instrument in the cord circuit at the operator position I2 and thetoll line extending to the exchange B, the loop circuit, including the telephone instrument in the cord circuit 50 at the operator position I2. being operatively associated with the `previously traced loop circuit, extending between the windings 11 and 18 of the repeater 14 and the windings 65 and 66 of the repeater 64, by way of the previously traced loop circuit extending between the windings 31 and 39 of the repeater I3 and the windings 61 and 68 of the repeater 64.` Also the windfings 11 and 18 of the repeater 14 are operatively associated with the windings 15 and 16 thereof connected to the toll line 10 extending to the exchange B. In the event the toll line 16 is busy at this time, voice frequency current is diverted therefrom by way of the various loop circuits previously traced to the receiver of the telephone instrument in the cordcircuit 58 at the operator position I2 and the toll operator thereat hears the conversation. i i

Onithe other hand, in the event the toll line 10 is idle at this time; the toll operator at the operator position I2 does not hear a conversation. The toll operator at the operator position I2 then actuates the ring key in the cord circuit 50 there at; thereby to complete the previously traced circuit for conducting alternating ringing current over a portion of the previously traced loop cir cuit extendingibetween the windings 36 and 38 of the repeater I3 and the `cord circuit 50. The alternating ringing current traversing the windings 36 and 38 of the repeater I3i`induces a similar alternating ringing current in thewindings 31 and 39 of the repeater I3 which ringing current traverses the previously traced loop circuit extending between the windings 31 and 38 of the repeater I3 and the windings 61 and 68 of the The alternating ringing current traversing the windings 61 and 68 of the repeater 64 induces a similar alternating ringing current in the windings 65 and 66 of the repeater 64 which ringing current traverses the previously traced loop circuit extending betweenv the windings 11 and 18 of the repeater 14 and the windings 65 and 66 ofthe repeater 64. The alternating ringing current traversing the windings 11 and 18 of the repeater 14 induces a similar alternating ringing current in the `windings 15 and 16 of the repeater 14 which ringing current traverses a loop circuit extending between the windings of the repeater I1 and the windings`15 and 16 of the repeater 14.` The alternating ringing current traversing the last-mentioned windings of the repeater I1 induces a similar alternating ringing current in the associated windings of the repeater I1 which ringing current traverses a loop circuit extending between the last-mentioned windings of the repeater I1 `and the winding of the signal at the operator position I6. The alternating ringing current traversing the winding of the signal at the operator position I6 actuates the signal, thereby to indicate to the toll operator at the operator position I6 that a call is extended to the exchange B.` f i l The toll operator at the operator position I6 answers the call by insertingjthe plug of the cord circuit thereat into the answer `jackat the operator position I6; When the plug of the cord cir-- cuit isinserted into the answer jack at the operator position I6 the previously mentioned loop circuit for energizing the winding or the "signal thereat is interrupted, thereby to arrestfurther operation of the signal; Finai1y,theto11 opera-A tor at the operator position I6 actuates the talk key in the cord circuit thereat, thereby to complete a loop circuit between the windings of the repeater I1 and the telephone instrument in the cord circuit at the operator position I6. At this time `a two-way communication connection is established between the telephone instrument in the cord circuit 50 at the operator position I2 and the telephone instrument in the cord circuit at the operator position I6, thereby to permit the toll operators at the operator positions I2 and I6 in the exchanges C and B, respectively, to communicate with each other in either direction.

The release `of this established connection between the exchanges C and B is primarily under the control of the toll operator at the operator position I2 in the exchange C and is effected by the toll operator thereat by removing the plug 5I of the cord circuit 56 from the call jack 4D. When the plug 5I is removed from the call jack 40 the switch springs 43 and 44 thereof are actuated into disengagement, thereby to interrupt the previously traced path for connecting the ungrounded positive terminal of the battery 45 to the conductor G21. When the ungrounded positive terminal of the battery 45 is disconnected from the conductor G21, the previously traced circuit including the simplen link provided by the toll line 6B and the windings of the repeaters 64 and I3 associated therewith for energizing the winding of the relay RI 05 is inter rupted, whereupon the relay RI 65 restoresi Upon restoring, the relay RIOS interrupts, at RAIIH and at RAIGB, the previously traced loop circuit extending between the windings 11 and 18 ci the repeater 14 and the windings 65 and 66 of the repeater 64. Finally, the toll operators at the operator positions I6 and I2 actuate the talk keys in the respective cord circuits thereat in order to disconnectthe telephone instruments therein from the plugs of the respective cord circuits at the respective operator positions.

A call which is to be extended from the exchange A to the exchange C is initiated by' the toll operator at the operator position I4 in the exchange A upon inserting the plug of the cord circuit thereat into a proper one of the call jacks thereat, thereby to cause the ungrounded positive terminal of a battery, the negative terminal of which is grounded, to be connected to a conductor, not shown, extending to the neutral point between the windings of the repeater I5, included in the previously mentioned loop circuit extending between the last-mentioned windings of the repeater I5 and the windings 85 and 86 oi the repeater 84. This application of positive battery potential to the conductor mentioned completes a circuit including a simplex link provided'by the toll line 86 and the windings of the repeaters I5 land 64 associated therewith for energizing .the relay R96. The last-mentioned circuit extends from the positive terminal of battery by way of the conductor mentioned to the neutral point between the windings mentioned of the repeater I5 and from the neutral point between the windings and 86 of the repeater 84 by way of theconductor C83, the winding of the relay R96, the rectifier 96 and the conductor C99 to ground, the first-mentioned neutral point between the windings of the repeater I5 being connected to the last-mentioned neutral point between the windings of the repeater 84 by' way of a path extending from the firstdnentioned neutral pointover one of the windings of the repeater I6, the line conductor CBI of the toll to the last-mentioned neutral point, and by way of a path extending from the rst-mentioned neutral point over another winding of the repeater I5, the line conductor C82 of the toll line 8G and the winding 85 of the repeater 84 to the last-mentioned neutral point. It is noted that the rectier 96 readily conducts current over the above-traced circuit in the direction indicated, thereby eiectively to short-circuit the winding of the relay R95; while the rectifier 9| blocks the passage of current therethrough when current is conducted over the above-traced circuit in the direction indicated. Accordingly, at this time, the relay R95 is not operated and the relay R99 is operated. Upon operating, the relay R90 completes, at RA92 and at RA93, a loop circuit extending between the windings 87 and 88 of the repeater S4 and the windings 65 and E6 of the Arepeater 64. The last-mentioned loop circuit extends from the conductor CI by way of the windings 81 and 83 of the repeater 84, the conductor CI23, RA93, the conductor CI24, the windings 65 and B5 of the repeater 64, the conductor CI2I and RA92 to the Iconductor CI2D.

After inserting the plug of the cord circuit into the call jack at the operator position I4, the toll operator actuates the talk key in the cord circuit thereat, thereby to complete a loop circuit between the telephone instrument in the cord circuit thereat and the windings of the repeater I5.

At this time a connection is established between the telephone instrument in the cord circuit at the operator position I4 and the toll line y.-

60 extending to the exchange C, in an obvious manner. In the event the toll line 60 is busy at this time, voice frequency current therefrom is diverted by way of the various loop circuits previously traced to the receiver of the telephone instrument in the cord circuit at the operator position I4 and the toll operator thereat hears the conversation.

On the other hand, in the event the toll line 60 is idle at this time, the toll operator at the operator position I4 does not hear a conversation. The toll operator at the operator position I4 then actuates the ring key in the cord circuit thereat, thereby to complete a circuit for conducting alternating ringing current over aportion of the loop circuit extending between the operator position I 4 and the repeater I5, thereby to cause ringing current to be induced in the loop circuit extending between the repeaters I5 and 84. The alternating ringing current traversing the last-mentioned loop circuit causes ringing current to be induced in the loop circuit extending between the repeaters 84 and 54; and the alternating ringing current traversing the lastmentioned loop circuit causes ringing current to be induced in the loop circuit extending between the repeaters 64 and I3. The alternating ringing current traversing the last-mentioned loop circuit causes ringing current to be induced in the windings and-38 of the repeater I 3, thereby to complete a circuit for energizing the winding of the signal 24. The circuit for energizing the winding of the signal 24 extends from the conductor C25 by way of the winding of the signal 24, the switch springs 23 and 22 of the answer jack 20, the conductor C25 and the windings 38 and 36 of the repeater I3 to the conductor C2 5. The alternating ringing current traversing the winding of the signal 24 causes the signal to be actuated, @thereby to indicate to the toll operator at the line 80 and the winding 85 of the repeater 84 operator position I2 that a call is on the toll line 60.

The toll operator at the operator position I2 then answers the call by inserting the plug 5I of the cord circuit thereat into the answer jack 20. When the plug 5I of the cord circuit 50 is inserted into the answer jack 20 the switch springs 22 and 23 are actuated into disengagement, thereby to interrupt the previously traced `circuit for energizing the signal 24. The toll operator at the operator position I2 then actuates the talk key in the cord circuit 59, thereby to complete a loop circuit between the telephone instrument in the cord circuit 50 thereat and the windings 36 and 38 of the repeater I3. The lastmentioned loop circuit extends from the conductor C25 by way of the windings 3S and 38 of the repeater I 3, the conductor C26, the jack ring 22, the plug ring 53, the talk key and telephone instrument in the cord circuit 50, the plug tip 52 and the jack tip 2I to the conductor C25. At this time a two-way communication connection is established between the operator positions I 4 and I 2 in the exchanges A and C, respectively. ,The release of this established connection is primarily under the control of the toll operator atthe operator position I 4 in the exchange A and is eiected when the toll operator thereat withdraws the plug of the cord circuit thereat from the associated call jack, thereby to interrupt the previously traced circuit including the simplex link provided by the toll line 8D and the windings of the repeaters I5 and 84 for energizing the winding` of the relay R90, whereupon the relay R90 restores. Upon restoring, the relay R90 interrupts, at RA92 and at RA93, the previously traced loop circuit extending between the windings 8'I and 88 of the repeater 84 and the windings and 56 of the repeater 64. Subsequently, the toll operators at the toll operator positions I4 and I2 in the exchanges A and C, respectively, return the talk keys in the respective cord circuits thereat to their normal positions, thereby to disconnect the respective telephone instruments from the associated cord circuits,

From the foregoing description of the manner of extending and releasing connections between the exchanges C and A, C and B and A and C, it will be understood that connections may be extended and released between the exchanges A and B, B and A, and B and C, in a similar manner.

More particularly, in order to extend a connection between the exchange A and the exchange B, the toll operator at the operator position I4 inserts the plug of the cord circuit thereat into the proper call jack, thereby to complete a path for connecting the ungrounded negative terminal of a battery, the positive terminal of which is grounded, to a conductor, not shown, extending to the neutral point between the windings of the repeater I 5. When the negative terminal of battery is connected to the conductor mentioned, a circuit including a simplex link provided by the toll line and the repeaters I 5 and 84 associated therewith for energizing the winding of the relay R95 is completed. The last-mentioned circuit extends from ground by way of the conductor C99, the winding of the relay R95, the rectifier 9| and the conductor C83 to the neutral point between the windings and 8S of the repeater 84, -the neutral points between the respective windings of the repeaters 84 and I5 being connectedtogether by way of a simplex circuit inlcluding the toll line 80. It is noted that the rectifier 9|v readily conducts current over the above-traced circuit in the direction indicated, thereby effectively to short-circuit the winding of the relay RSU; while the rectifier 96 blocks the passage of current therethrough when current is conducted over the above-traced circuit in the direction indicated. Accordingly, at this time, the relay R90; is not operated and the relay R95 is operated.

Upon operating, the relay R95 completes, at RAQI and at RASS, a loop circuit extending between the windings 81 and 88 of the repeater 84 and the windings 'II and 'I8 of the repeater 14. The last-mentioned loop circuit extends from the conductor CI20 by way ofthe windings 81 and v88 ot the repeater 84, the conductor CI23, RABB, the conductor C125', the windings 18 and 'I1 of the repeater 14, the conductor CI22` and` RA91 Ato the conductor CI20. At this time a connection is established between the toll lines 880 and I in a manner similar to that previously explained. The manner of signaling thetoll operatorjat the operator position I6 in the exchange B and the manner of releasing the established connection between the exchanges A and B are the same as previously described.

More particularly, in order" to' extend a connection between the exchange B and the exchange A, the toll operator at the operator position I6 inserts the plug ofthe cord circuit thereinto the proper call jack, thereby to complete a path fcrconnecting the ungrounded negative terminal of a battery, the positive terminal of which isgroundedi, to a conductor, not shown, extending to the neutral point between the windings of the repeater I1. When the negative terminal of battery is connected to the conductor mentioned, a circuit including a simplex link provided by the toil line 'IUS and the repeaters I'I and 'I4 asso-` ciated therewith `fer energizing the winding of the. relay Rllll is completed. The last-mentioned. circuit extends from ground by way of the conductor CIJI H; the windingof the relay RI ID, the rectifier H16- and the conductor C13 to the neutral point `between the windings I and 'I6 of the repeater 14, the neutral points between theA respective windings of the repeaters 14 and IFI.; being connected together by way of a simplex circuit` including the toll-i line 10. It is noted that 'the rectifier H6 readily conducts current over the above-traced: circuit in the direction indicate@ thereby eecti-velyto short-circuit the winding: ofthe relay RI.I'5;1 While the rectifier II I blocksflthe. passage of current therethrough when cmtrentis` conducted overthe above-traced circuit in. the: direction indicated. Accordingly, at this time,l the relay RME` is not operated and therelay Rttisoperated.

. Upony operating, the relayl RIID completes, at RAIIZ and at RAIIS, a loop circuit extending between the windings TI and I8 oi the repeater 'I4 and the.- windings. BJI: andi 88 o1.'V the repeater 8.4, The.y `last-mentioned loep` circuity extends from the conductor CI2I)` by wayot the windings 831v and 88f of the repeater 84,4 the conductor CH3, RAUS, the conductor C125, the winding-s 'I8 and 'H- of the repeater 1.4,. the conductor Cl22 andV RAI-I2:` to the. conductor CI20. At this time a connection is: established` between the toll lines l0 and 8UJ ini a manner similar to that previously explained. The manner of` signaling the` toll operator at the operator position I4 in the exchange Ai and the manner of` releasing the establislflect` connection between the exchanges, B. andfAare the.:y same previously described..

More particularly, in order to extend a. connection between the exchanges B and C, the toll operator at the operator position I6 inserts the plug of the cord circuit thereat into the proper call jack, thereby to complete a path for connecting the ungrounded positive terminal` of a battery, the negative terminal of which is grounded, to a conductor, not shown, extending to the neutral point between the windings of the repeater I1. When the positive terminal of. but tery is connected to the conductor mentioned, acircuit including a simplex link provided by the toll line 'I0 and the repeaters I1 and I4 associated therewith for energizing the winding of the relay' RIIE` is lcompleted. The last-,mentioned circuit extends from the positive terminal of battery connected to the conductor mentioned to the neutral point between the windings of the repeater I1 and from the neutral point between the windings -I5 and 1,6 of the repeater 'Mby way of the conductor C13, the winding of the relay RHS, the rectier III and the conductor CI I9 to ground, the neutral points between.. the respective windings of the repeaters II andv I4 being connected together by way of. a simplex circuit including the toll line 10. It is noted that `the rectifier III readily conducts current over the above-traced circuit inthe direction im dicated, thereby effectively to short-circuit the winding of the relay RII'U; while theY rectifier IIB blocks the passage of current therethrough when current is conducted over the above-traced circuit in the direction. indicated'. Accordingly; at this time, the relay RI IU is not operated and the relay RI I5 is operatedr Upon operatingthe relay RI I5 completes, at RAI ll and` at RAI I8, a. loop circuit between the windings I1 and 'I8 of the repeater 'I4Y and the windings 65 and EESv of the repeater 64. The lastmentionedr loo-p circuit extends from the conductor CI22 by way of the windings 'I1 and I8 of the` repeater 14, the conductor CI25, RAIN, the conductor CIZ, the windings 68V and. 65 of the repeater 84, the conductor C|-2I and RAI I'l to the conductor CI22. At this time a connection is established between the toll lines 'I0 and in a manner similar to that previouslyY explained. The man-nerof signaling the toll operator at the operator position I2` in the exchange C and the manner of releasing` the established connection between the exchanges B and C are the: same as previously described.

While there has been described what is at present considered tor be the preferred embodiment of the invention, it will be understood that various modifications may be made therein without departing from the invention and it is intended t'o cover in the appended claims all such modications as fall 'within the true spirit and scope of the invention.

What isclaimed. is:

1. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, iirst and second lines at said switchi-ng center, switching apparatus at said' switching center andv operative selectively to associate said trunk with said first and second lines for communication thereover, apparatus at said switching center and responsive to first and second continuous voltages" of different characteristics impressed upon said trunk for controlling selectively the operation of said switching apparatus, and apparatus said exchangeoperative tor causesaid, first and secondl continuous voltages to be impressed selectively upon said trunk.

2. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, iirst and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk with said first and second lines for communication thereover, apparatus at said switching center and responsive to iirst and second voltages of difierent polarity impressed upon said trunk for controlling selectively the operation of said switching apparatus, and apparatus in said exchange operative to cause said rst and second voltages to be impressed selectively upon said trunk.

3. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, rst and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk with said rst and second lines for `communication thereover, apparatus at said switching center and including a circuit network and means controlled I in accordance with the direction of current now in said circuit network for governing selectively the operation of said switching apparatus, a circuit including said trunk for conducting current to said circuit network, a telephone instrument in said exchange, and apparatus in said exchange operative to associate said telephone instrument with said trunk and to complete said circuit and selectively to determine the direction of the current conducted to said circuit network 4. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, first and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk with said first and second lines for communication thereover, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current ow in said circuit network for governing selectively the operation of said switching apparatus, a circuit including said trunk for conducting current to said circuit network, a telephone instrument in said exchange, rst and second jacks in said exchange, means including said rst jack for operatively associating said telephone instrument with said trunk and for completing said circuit to conduct current in one direction to said circuit network, and means including said second jack for operatively associating said telephone instrument with said trunk and for completing said circuit to conduct current in the opposite direction to said circuit network.

5. In a telephone system, an exchange, a switching center, a trunk having two line conductors and extending between said exchange and said switching center, first and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk with said rst and second lines for communication thereover, apparatus at Said switching center and including a circuit network and means controlled in accordance with the direction of current :dow in said circuit network for governing selectively the operation of said Switching apparatus, means including said trunk and impedance elements in said exchange and at said switching center connected to the line conductors of said trunk for providing a simplex link, said circuit network having two terminals, one terminal of said circuit network being connected to ground and the other terminal thereof being connected to said simplex link, a telephone instrument in said exchange and having a plug associated therewith, rst and second jacks in said exchange and associated with the line conductors of said trunk, said telephone instrument being operatively associated with said trunk when said plug is inserted into either one of said jacks, means controlled by the insertion of said plug into said rst jack for connecting the ungrounded positive terminal of a grounded source of current to said simplex link, and means controlled by the insertion of said plug into said second jack for connecting the ungrounded negative terminal of a grounded source of current to said simplex link.

6. In a telephone system, an exchange, a switching center, a trunk having two line conductors and extending between said exchange and said switching center, first and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk with said rst and second lines for communication thereover, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current fiow in said circuit network for governing selectively the operation of said switching apparatus, means including said trunk and impedance elements in said exchange and at said switching center connected to the line conductors of said trunk for providing a simplex link, a circuit including said simplex link for conducting current to said circuit network, apparatus in said exchange operative to complete said circuit and selectively to determine the direction of the current conducted to said circuit network, and means in said exchange for projecting alternating signal current over said trunk and the one of said lines associated therewith.

7. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, rst and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk with said rst and second lines for communication thereover, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switching apparatus, a circuit including said trunk for conducting current to said circuit network, a telephone instrument in said exchange, apparatus in said exchange operative to associate said telephone instrument with said trunk and to complete said circuit and selectively to determine the direction of the current conducted to said circuit network, and means in said exchange for projecting alternating signal current over said trunk and the one of said lines associated therewith, said circuit and said circuit network being so connected and arranged that there is substantially no interference with the projection of alternating signal current and the iiow of voice frequency current over said trunk and the one of said lines associated therewith,

8. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, switching apparatus at said switching center and operative selectively to perform different switching functions, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switchingapparatus, a circuit including said trunk for conducting current to said circuit network, and apparatus in said exchange operative to complete said circuit and selectively to determine the direction of the current conducted to said circuit network.

9. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, first and second lines at saidswitching center, apparatus at said switching center and responsive to rst and second continuous voltages of di'lferent characteristics impressed upon said trunk line for selectively associating said trunk line with said first and second lilies for signaling thereover, and apparatus in said station operative to cause said first and second voltages to be impressed selectively upon said trunk line.

ll). In a signaling systern, a station, a switching center, a trunkline extending between said station and said switching center, first and second lines at said switching center, apparatus at said switching center and responsive to first and second voltages of diiierent polarity impressed upon said trunk line for selectively associating said trunk line with said first and second lines for signaling thereover, and apparatus in said station operative to cause said rst and second voltages to be impressed selectively upon said trunk line.

1l. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, first and second lines at said switclling center, switching apparatus at said switching center and operative selectively to first and second positions, means responsive to the operation of said switching apparatus to said rst position for associating said trunk line with said rst line for signaling thereover, means responsive to the operation of said switching apparatus to said second position for associating said trunk line with said second line for signaling thereover, apparatus at said switching center and responsive to rst and second voltages of' different characteristics impressed upon said trunk line for selectively operating said switching apparatus to said first and second position, and apparatus in said station operative to cause `said first and second voltages to be impressed selectively upon said trunk line.

12,. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, rst and second lines at said switching center, switching apparatus at said switching center and operative selectively to first and second positions, means responsive to the operation of said switching apparatus to said rst position for associating said trunk: line with said first line for signaling thereover, means responsive to the operation of said switching apparatus to said second position for associating said trunk line with said second line tor signaling thereover, control apparatus at said switching center and responsive to a voltage of one polarity impressed upon said trunk line for causing said switching apparatus to he operated to said first position and responsive to a voltage of opposite polarity impressed upon said trunk impressed selectively upon said trunk line.

13. in a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, first and second lines at said switching center, relay means at said switching center and operative selectively to rst and second positions, means controlled by the operation of said relay means to` said first position for associating said trunk line with said rst line for signaling thereover and controlled by the operation of said relay means to said second position for associating said trunk line with said second line for signaling thereover, a circuit including said trunk line for energizing said relay means, said relay means being so connected and arranged that it is operated to said first position when it `is energized with current traversing said circuit in one direction and is operated to said second position when it is energised with current traversing said circuit in an "opposite direction, and apparatus in said station operative to complete said circuit andselectively to determine the direction of the current traversing said circuit.

14. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, first and second lines at said switching center, rst and second relays at said switching center, rneans controlled by the operation of said rst relay for associating said trunk line with said rst line for signaling thereover, means controlled by the operation of said second relay for associating said trunk line with said second line for signaling thereover, a circuit including said trunk line for energizing said first and second relays, said iirst and second relays being so connected and arranged that said first relay is operated and said second relay is not operated when a current traverses said circuit in one direction and that said rst relay is not operated and said second relay is operated when a current traverses said circuit in an opposite direction, and apparatus in said station operative to complete said circuit and selectively to determine the direction of the current traversing said circuit.

15. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, first and second lines at said switching center, first and second relays at said switching center, means controlled by the operation of said rst relay for associating said trunk line with said first line :for signaling thereover, means controlled by the operation oi said second relay for associating said trunk line with said second line for signaling thereover, each of said relays having an operating winding, the winding of said relays being connected in series circuit relationship, a rst uni-directional current conducting device connected in parallel circuit relationship with the winding of said first relay, a second uni-directional current conducting device connected in parallel circuit relationship with the winding of said second relay, a circuit including said trunk line forenergizing the windings of said first and second relays, said relays and said devices being so connected and arranged that the winding of said iirst relay is effectively energized and the winding of said second relay is effectively shortcircuit-ed when a current traverses said circuit in one direction and that the winding of said first relay is effectively short-circuited and the winding of said second relay is effectively energized when a current traverses said circuit in an cpposite direction, and apparatus in said station operative to complete said circuit and selectively to determine the direction of the current traversing said circuit.

16. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, iirst and second lines at said switching center, switching apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switching apparatus, a circuit including said trunk line for conducting current to said circuit network, and apparatus in said station operative to complete said circuit and selectively to determine the direction of the current conducted to said circuit network.

17. In a signaling system, a station, a switching center, a trunk line having two line conductors and extending between said station and said switching center, iirst and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunkline with said iirst and second lines for signaling thereover, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switching apparatus, means including said trunk line and impedance elements in said exchange and at said switching center connected to the line conductors of said trunk line for providing a simplex link, a circuit including said simplex link for conducting current to said circuit network, and apparatus in said station operative to complete said circuit and selectively to deterrriine the direction of the current conducted to said circuit network.

18. In a signaling system, a station, a switching center, a trunk line extending between said station and said switching center, rst and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk line with said iirst and second lines for signaling thereover, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current ow in said circuit network for governing selectively the operation of said switching apparatus, said circuit network having two terminals, one of the terminals of said circuit network being connected to ground and the other terminal thereof being connected to said trunk line, and apparatus in said station operative selectively to connect the ungrounded positive terminal of a grounded source of current and the ungrounded negative terminal of a grounded source of current to said trunk line.

19. In a signaling system, a station, a switching center, a trunk line having two line conductors and extending between said station and said switching center, first and second lines at said switching center, switching apparatus at said switching center and operative selectively to associate said trunk line with said iirst and second lines for signaling thereover, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switching apparatus, means including said trunk line and impedance elements in said station and at said switching center connected to the line conductors of said trunk line for providing a simplex link, said circuit network having two terminals, one terminal of said circuit network being connected to ground and the other terminal thereof being connected to said simplex link, and apparatus in said station operative selectively to connect the ungrounded positive terminal of a grounded source of current and the ungrounded negative terminal of a grounded source of current to said simplex link.

20. In a telephone system, a plurality of exchanges, a switching center, a plurality of trunks respectively extending between said exchanges and said switching center, switching apparatus at said switching center and operative selectively to perform different switching functions, a plurality o1" control apparatus at said switching center and associated with said switching apparatus, each of said control apparatus including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively certain of the operations of said switching apparatus, a plurality of circuits respectively including said trunks for conducting current to the control networks of the respective control apparatus, and apparatus in said exchanges respectively operative to complete respective ones of said circuits and selectively to determine the direction of the current conducted to the circuit networks of the respective control apparatus.

2l. In a telephone system, rst and second and third exchanges, a switching center, first and second and third trunks respectively extending between said rst and second and third exchanges and said switching center, switching apparatus at said switching center, said switching apparatus being so connected and arranged that it is responsive to first and second voltages of different characteristics impressed upon said rst trunk for selectively associating said iirst trunk with said second and third trunks for communication thereover and that it is responsive to first and second voltages of different characteristics impressed upon said second trunk for selectively associating said second trunk with said rst and third trunks for communication thereover and that it is responsive to first and second voltages of diirerent characteristics impressed upon said third trunk for selectively associating said third trunk with said first and second trunks for communication thereover, and apparatus in each of said exchanges operative to cause said first and second voltages to be impressed selectively upon the associated trunk.

22. In a telephone system, iirst and second and third exchanges, a switching center, rst and second and third trunks respectively extending between said first and second and third exchanges and said switching center, switching apparatus at said switching center, said switching apparatus being so connected and arranged that it is responsive to rst and second voltages of different polarity impressed upon said first trunk for selectively associating said first trunk with said second and third trunks for communication thereover and that it is responsive to rst and second voltages of diiierent polarity impressed upon said second trunk for selectively associating said second trunk with said irst and third trunks for communication thereover and that it is responsive to first `and second voltages of dilierent polarity impressed upon said third trunk for selectively associating said third trunk with said iirst and second trunks for communication thereover, and apparatus in each of said exchanges operative to cause said first and second voltages to be impressed selectively upon the associated trunk.

23. In a telephone system, irst and second yand third exchanges, a switching center, iirst and second and third trunks respectively extending between said rst and second and third exchanges and said switching center, first and second and third switching apparatus at said switching center and respectively associated with said first and second and third trunks, each oi said switching apparatus being operative selectively to associate the trunk associated therewith with the other twoy trunks for communication thereover, first and second and third control apparatus at said switching center and respectively associated with said first and second and third switching apparatus, each of said control apparatus including a circuit network and means controlled in accordance with the direction of current iiow in said circuit network for governing selectively the operation of the associated switching apparatus, rst `and second and third circuits respectively including said irst and second and third trunks for conducting current `to `the circuit networks of the respective control apparatus, and apparatus in said first and second and third exchanges respectively operative to complete said first and second and third circuits and selectively to determine the direction ci `the current conducted to the circuit networks of said lirst and second and third conltrol apparatus.

In a signaling system, a plurality of stations, a switching center, a plurality of trunk lines respectively extending between said stations and said switching center, switching apparatus at said switching center, said switching vapparatus being so connected and arranged that it is responsive to iirst and second voltages ci diferent characteristics impressed upon yany one of said trunk lines for selectively associating said one trunk line with two other of vsaid `trunk lines :for signaling therecver, and apparatus in each of said stations operative to cause said first and second voltages to be impressed selectively upon the associated trunk line.

25. In a signaling system, a plurality oi stations, a switching center, a plurality of trunk lines respectively extending between said stations and said switching center, switching apparatus at said switching center, said switching apparatus being so connected and `arranged that it is responsive to first land second voltages oi different polarity impressed upon any one of said trunk lines for selectively associating said one trunk line with two other of said trunk lines for signaling thereover, and apparatus in each of said stations operative to cause said first and second voltages to be impressed selectively upon the associated trunk line.

26. In a signaling system, a plurality ol. stations, a switching center, a plurality ci trunk lines respectively extending between said stations and said switching center, a plurality of switching apparatus at said switching center and respectively associated with said trunk 1lines, each of said switching apparatus being operative selectively to 'associate the trunk line associated therewith with two other trunk lines for signaling thereover, a plurality of control apparatus at said switching center and respectively associated with said switching apparatus, each of said control apparatus including a circuit network and means controlled in accordance with the direction of current flow in said circuit network 'for governing selectively the operation of the associated switching apparatus, a plurality of circuits respectively including said trunk lines for conducting current to the circuit networks oi the respective control apparatus, and apparatus in said stations respectively operative to complete respective ones of said circuits and selectively to determine the direction of the current conducted to the circuit networks oi the respective control apparatus.

27.111 a telephone system, an exchange, a switching center, a first trunk extending `cetween said exchange and said switching center, second and third trunks extending to said switching center, said first trunk including two line conductors. iirst second and tjhird repeaters at said switching center respectively associated with said iirst second and third trunks, another repeater in said exchange associated with said iirst trunk, switching apparatus at Said switching center and operative selectively to associate said first repeater with said second and third repeaters, thereby selectively and operatively to connect said first trunk: to said second and third trunks, apparatus `at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switching apparatus, means including said iirst trunk and said irst and other repeaters for providing a simplex link, a circuit including said simplex link for conducting current to said circuit network, a telephone instrument in said exchange, and apparatus in said exchange operative to associate said telephone with said other repeater and to complete said circuit and selectively to determine the direction of the current conducted to said circuit network.

28. In a teieplione system, first and second and third exchanges, a switching center, first and second and third trunks respectively extending `between said iirst and second and third exchanges and switching center, each of said trunks including two line conductors, first and second and third repeaters at said switching center respectively `associated with said nrst second and third trunks, first and second .and third additional repeaters in said first and second and third exchanges and respectively associated with said first and second and third trunks, first 'and second and third switching apparatus at said switching center and respectively associated with said inst-mentioned first and second and third repeaters, each oi said switching apparatus being operative selectively to associate the first-mentioned repeater associated therewith with the other two first-mentioned repeaters, thereby selectively and operatively to connect each trunk to the other two trunks, first and second and third control apparatus vat said switching center and respectively associated with said .first and second and third switching apparatus, each of said control apparatus including a circuit network and means controlled in accordance with the direction of current flow in said circuit network ior governing selectively the operation of the associated switching apparatus, means including said rst and second and third trunks and said nrst and second and third rst-mentioned and additional repeaters respectively associated therewith for respectively pro- Vidng iiist and second and third simplex links, first and second and third circuits respectively including said first and second and third simplex links for conducting current to the respective circuit networks of said first and second and third control apparatus, and apparatus in said rst and second and third exchanges respectively operative to complete said first and second and third circuits and selectively to determine the direction of the current conducted to the circuit networks of said rst and second and third control apparatus.

29. In a signaling system, a station, a switching center, a rst trunk line extending between said station and said switching center, second and third trunk lines extending to said switching center, said first trunk line including two line conductors, fir-st and second and third repeaters at said switching center respectively associated with said iirst and second and third trunk lines, another repeater in said station associated with said rst trunk line, switching apparatus at said switching center and operative selectively to associate said first repeater with said secc-nd and third repeaters, thereby selectively 'and operatively to connect said iirst trunk line to said second and third trunk lilies, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of said switching apparatus, means including said rst trunk line and said rst and other repeaters for providing a simplex link, va circuit including said simplex link for conducting current to said circuit network, and apparatus in said station operative to complete said circuit and selectively to determine the direction of the current conducted to said circuit network.

30. In a signaling system, a station, a switching center, a first trunk line extending between said station and said switching center, second and third trunk lines extending to said switching center, said first trunk line including two line conductors, rst and second and third repeaters at said switching center respectively associated with said first and second and third trunk lines, another repeater in said station associated with said rst trunk line, switching apparatus at said switching center and operative selectively to associate said iirst repeater with said second and third repeaters, thereby selectively and operatively to connect said first trunk line to said second and third trunk lines, apparatus at said switching center and including a circuit network and means controlled in accordance with the direction of current flow in said cir-cuit network for governing selectively the operation of said switching apparatus, means including said rst trunk line `and said rst and other repeaters for providing a simplex link, said circuit network having two terminals, one terminal of said circuit network being connected to ground and the other terminal thereof being connected to saidy simplex link, and apparatus in said station operative selectively to connect the ungrounded positive terminal of a grounded source of current and the ungrounded negative terminal of a grounded source of current to said simplex link.

3l, In a signaling system, a plurality ol stations, a switching center, a plurality of trunk lines respectively extending between said stations and said switching center, each of said trunk lines including two line conductors, a plurality of repeaters at said switching center respectively associated with said trunk lines, a plurality of additional repeaters in said stations and respec-v tively associated with said trunk lines, a plurality of switching apparatus at said switching center and respectively associated with said rstmentioned repeaters, each of said switching apparatus being operative selectively to associate the rst-mentioned repeater associated therewith with two other of the first-mentioned repeaters, thereby selectively and operatively to connect each trunk line to two other trunk lines, a plurality of control apparatus at said switching center and associated with said switching apparatus, each of said control apparatus including a circuit network and means controlled in accordance with the direction of current flow in said circuit network for governing selectively the operation of the associated switching apparatus, means including said trunk lines and said firstmentioned and additional repeaters respectively associated therewith for respectively providing a plurality of simplex links, a plurality of circuits respectively including said simplex links for conducting current to the control networks of the respective control apparatus, and apparatus in said stations respectively operative to complete respective ones of said circuits and selectively to determine the direction of the current conducted to the circuit networks of the respective control apparatus.

32. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, first and second lines at said switching center, switching apparatus at said switching center, said switching apparatus being operable selectively to associate said trunk with said rst and second lines for communication thereover and restorable to disassociate said toll trunk from said first and second lines, apparatus at said switching center and responsive to the impression of first and second continuous voltages of different characteristics upon said trunk for causing selective operations of said switching apparatus and responsive to the removal of said first continuous voltage or said second continuous voltage from said toll trunk for causing restoration of said switching apparatus, and means in said exchange selectively operable to cause said rst and second continuous voltages to be impressed selectively upon said trunk and to cause said first continuous voltage or said second continuous voltage to be removed from said trunk.

33. In a telephone system, an exchange, a switching center, a trunk extending between said exchange and said switching center, first and second lines at said switching center, switching apparatus at said switching center, said switching apparatus being operable selectively to associate said trunk with said first and second lines for communication thereover and restorable to disassociate said trunk from said first and second lines, apparatus at said switching center and responsive to the impression of first and second continuous voltages of different characteristics upon said trunk for causing selective operations of said switching apparatus and responsive to the removal of said rst continuous voltage or said second continuous voltage from said trunk for projecting alternating ringing current over said trunk and the one of said lines associated therewith while either said rst continuous voltage or said second continuous voltage is 5 impressed upon said trunk.

CLARENCE E. LOMAX. 

